Reproduction and cyst formation in Scrippsiella precaria (Dinophyceae)

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Abstract
The life cycle of Scrippsiella precaria Montresor & Zingone was studied using a clonal culture. At 25[ddot]C and 100 μE/m2/s a maximum growth rate (kmax) of 0.53 div./d was calculated. Vegetative reproduction takes place through ecdysis. The naked protoplast emerges from a non motile cell characterized by a thin emphiesma. In some cases, cell division occurs after the loss of the parental amphiesma. In other cases, the division process is nearly complete when the two daughter cells are freed. In standard culture conditions, resting cyst formation was observed toward the end of the log growth phase. Cysts developed within a non-motile form, similar to the one preceding ecdysis. Attempts to observe conjugation and zygote formation were unsuccessful. Smaller, less pigmented cells were observed attached in the sulcal region. In all experiments conducted so far these cells, which we supposed to be gametes in analogy with other dinoflagellates, were not seen to fuse. The characteristics of the life cycle of S. precaria are compared with those of other dinoflagellates.